This invention relates in general to digital medical imaging, and more particularly to a method of automatically determining the parameters used in creating a tone-scale look-up table to enhance a digital medical image for output presentation.
The tone-scale of a digital image is responsible for controlling the contrast and brightness characteristics of the image and is manifested in the form of a look-up table (LUT) that maps the input pixel values of the image (e.g., log exposure) to the appropriate output representation such as density or luminance. Automatic tone-scale algorithums are used today for the purpose of determining the optimal tone scale of the image and the parameters which control these algorithums are many. U.S Pat. No. 5,633,511, issued May 27, 1997, inventors Lee et al., discloses a tone scale algorithum which utilizes image activity measures as a means of determining the appropriate region of interest and then constructs a visually optimized tone-scale. This new image activity measures algorithum uses an entirely different set of parameters than the prior methods which used input code value histograms and image independent tone scale curves. In order to make the installation of the image activity algorithum transparent to the users, it is necessary to determine what parameters would achieve the same tone scale, and therefore the same overall look, as the old tone-scale algorithum. In a similar fashion, a tone-scale of unknown origin can be approximated using this method to determine appropriate parameters.
According to the present invention, there is provided a method of automatic determination of preferred tone-scale parameters for digital radiographic images comprising of:
providing an input digital medical image and an associated tone-scale LUT (a look-up table) associated; determining the contrast parameter which will result in preferred equivalent contrast with the associated tone-scale LUT; determining the toe and shoulder parameters which will result in preferred equivalent toe and shoulder with the associated tone-scale LUT; determining the density shift parameter which will result in preferred equivalent density with the associated tone-scale LUT; and generating a preferred LUT from the results of said three determining steps.
The invention has the following advantages.
1. Automatic determination of parameters to be used in creating a preferred tone scale in the form of a LUT.
2. A framework is provided for applying the technique to a suite of digital medical images.